linux-kernel - Re: [PATCH v4 1/2] xen-pciback: prepare for the split for stub and PV

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Date:   Mon, 27 Sep 2021 09:26:52 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>
Cc:     boris.ostrovsky@...cle.com, jgross@...e.com, julien@....org,
        sstabellini@...nel.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] xen-pciback: prepare for the split for stub and PV

On 27.09.2021 08:58, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
> 
> Currently PCI backend implements multiple functionalities at a time.
> To name a few:
> 1. It is used as a database for assignable PCI devices, e.g. xl
>    pci-assignable-{add|remove|list} manipulates that list. So, whenever
>    the toolstack needs to know which PCI devices can be passed through
>    it reads that from the relevant sysfs entries of the pciback.
> 2. It is used to hold the unbound PCI devices list, e.g. when passing
>    through a PCI device it needs to be unbound from the relevant device
>    driver and bound to pciback (strictly speaking it is not required
>    that the device is bound to pciback, but pciback is again used as a
>    database of the passed through PCI devices, so we can re-bind the
>    devices back to their original drivers when guest domain shuts down)
> 3. Device reset for the devices being passed through
> 4. Para-virtualised use-cases support
> 
> The para-virtualised part of the driver is not always needed as some
> architectures, e.g. Arm or x86 PVH Dom0, are not using backend-frontend
> model for PCI device passthrough. For such use-cases make the very
> first step in splitting the xen-pciback driver into two parts: Xen
> PCI stub and PCI PV backend drivers.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
> 
> ---
> Changes since v3:
> - Move CONFIG_XEN_PCIDEV_STUB to the second patch

I'm afraid this wasn't fully done:

> --- a/drivers/xen/xen-pciback/Makefile
> +++ b/drivers/xen/xen-pciback/Makefile
> @@ -1,5 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o
> +obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o

While benign when added here, this addition still doesn't seem to
belong here.

Jan